The present invention relates to the technical sector of manufacturing and it relates more particularly to a novel type of sheet support used as an element for transporting/conveying a mat which consists of a plurality of superimposed textile layers and which is intended to be cut up into the form of elementary panels of suitable shape in order subsequently to be joined together to produce the final product, such as a garment.
In the manufacturing field, it was proposed a very long time ago, as is especially apparent from FR-A-2,194,823 (corresponding to U.S. Pat. No. 3,495,492), to produce mats from textile structures (wovens or knits) intended for producing the manufactured article, which mats are transferred onto a cutting table.
During this operation, the fabric mat is placed on an air-permeable support and the cutting into elementary panels is carried out while creating a vacuum beneath the said table, so that the stack is perfectly held down during the cutting phase.
To avoid any movement of the elementary layers one with respect to another, and as is especially apparent from the aforementioned FR document and from FR-A-2,030,792 (corresponding to U.S. Pat. No. 3,495,492), the mat is covered in its upper part by an air-impermeable plastic film, thereby making it possible to compact the said mat during the cutting phase and avoiding any movement of the elementary layers one with respect to another.
With regard to the air-permeable supports which are used for supporting and transferring the mat consisting of continuous textile webs to the cutting station, various solutions have been proposed.
Thus, in FR 2,030,792 the support consists of a layer of material into which the tool can penetrate and which has channels or passages, thereby making it possible, with the vacuum exerted beneath the stack, to exert a suction action tending to hold down the material on the support table.
At the present time, the solution most often used consists in placing relatively rigid papers beneath the stack, these being perforated by stamping or notching, which have the essential advantage of being relatively inexpensive.
One of the problems which arise with such supports, therefore having channels or orifices allowing the air to flow out, stems from the fact that the suction is not uniformly distributed over the entire surface of the mat and, in some cases, there may therefore be irregular xe2x80x9ccompactionxe2x80x9d possibly resulting in defects in the cut panels.
In addition, the operation of forming the perforations is necessarily carried out after the manufacture of the paper and therefore results in the production of scrap.
The object of the invention is to propose the use of an air-permeable paper sheet as support element for a fabric stack on a manufacturing line, especially as support during the cutting phase. Such paper sheets are known per se, as revealed especially in Patents EP-A-616,074, EP-A-483,816 and EP-A-426,288 and have been proposed for producing articles having a great capacity for absorbing liquids, especially for the purpose of using them as wiping materials, hygiene articles, etc.
However, it has been found, and it is this which forms the subject of the invention, that it is possible to use such materials, which are inexpensive to manufacture, as support elements for a stack of fabrics (mat) on a manufacturing line, especially during the operation of cutting the said stack in order to produce elementary panels of suitable shape which are subsequently joined together to produce the final product.
It has been found, surprisingly, that the use of such a paper sheet, instead of the relatively rigid papers perforated by stamping or notching which were used in this technical field, helps to compact the stack under the action of the suction exerted during this cutting phase, ensures that the said mat slides easily on the table when placed thereon, prevents the textile structure from being marked, especially when it is a lightweight structure, and finally can be used practically for any type of textile structure.
For such an application, as paper sheet intended to serve as support, a sheet having, in its thickness, pores or fine perforations distributed over its entire surface will be used, the said sheet having a xe2x80x9cbulkxe2x80x9d or xe2x80x9cbodyxe2x80x9d expressed in cubic centimetres per gram of greater than 2.5, making it capable of allowing air to pass through it due to the effect of suction produced beneath its underside.
According to a first embodiment, the sheet structure has pores uniformly distributed over its entire surface, the said pores having a diameter of less than one millimetre and preferably between 50 and 150 microns.
According to a second embodiment, the pores or fine perforations are distributed in the form of patterns having a central region with high air permeability surrounded by a denser fibrous region with lower permeability.
Lastly, according to a final embodiment, the spacing between the centres of two consecutive patterns is less than 5 mm and preferably less than 3 mm, the central region with high permeability containing no fibres and having a total area of about 1 to 2 mm2.
The invention also relates to a process for obtaining a paper sheet that can be used as support element for a fabric stack on a manufacturing line, which consists in producing a filter paper directly on a paper machine, without any special modification, characterized in that, when obtaining the said paper:
during the preparation of the pulp, the cellulose fibres (wood pulp) are individualized without refining them excessively so as to maintain the maximum permeability;
the said pulp is fed to the machine with a very low concentration of less than one gram per liter, thereby making it possible to obtain a bulking sheet; and
the sheet produced is not compressed at the wet end of the machine so as to maintain its permeability.
Preferably, according to the invention, the permeability is maximized by subjecting the paper sheet produced, before it is dried, to a textiling treatment which consists in locally displacing the fibres by means of fluid jets or knives through a mesh having a coarse texture or through a perforated cylinder of the rotary printing cylinder type, or screen-printing type, so as to form patterns having a central region of high air permeability surrounded by a region with lower permeability.
In such a case of textiling treatment, the latter may have the consequence either of leaving in the central part only a small minority of fibres or of possibly producing a true perforation containing no fibres.
Such a treatment may be carried out on machines of known type, for example of the type forming the subject-matter in particular of FR-A-2,625,937.
Optionally, in order to improve the tear strength of the paper, it may be envisaged to incorporate synthetic or artificial fibres into the cellulose pulp, and to do so in an amount of 5 to 25%, the incorporation of such fibres moreover having a complementary effect of aerating the sheet and of consequently improving the permeability.
It has been found that an incorporation of less than 5% has no significant effect and that if this incorporation is greater than 25%, then, on the one hand, the manufacturing costs increase appreciably and, on the other hand and above all, it is absolutely essential to use additional binders.
Finally, as known in the paper field, it may be envisaged to incorporate an additional binder in an amount of about 5 to 25%, thereby making it possible to achieve chemical bonding, which improves the mechanical properties. Optionally, it could be envisaged to incorporate less than 5% of additional binders, but in this case the mechanical properties are hardly improved. Above 25%, the costs increase appreciably without any significant improvement in the properties.
As reinforcing fibres, it is possible to use synthetic fibres such as polyester, polyamide, polypropylene or polyethylene fibres, or even artificial fibres such as viscose fibres, or even natural fibres such as flax or cotton fibres for example.
The possible binders will be chosen from the following ingredients, possibly combined together:
conventional polymers also called xe2x80x9cLATEXxe2x80x9d, particularly of the acrylic type, ethylene-vinyl acetate type, vinyl acetate type, polyvinyl alcohol type, styrene-butadiene type, etc., and their associated copolymers by copolymerization or terpolymerization;
starch, carboxymethylcellulose, hexamethyl-cellulose;
polyamide or polyamine epichlorohydrin;
heat-bonding fibres.
The invention and the advantages that it provides will, however, be more clearly understood by means of the illustrative examples given below by way of indication, but implying no limitation, in which examples the properties of the paper according to the invention are compared with three specimens of conventional perforated papers referred to as Sp1, Sp2, Sp3, respectively.